Optimization of elevator systems take on the form of service time reduction, waiting time reduction, power consumption reduction, space usage reduction, etc.
In the area of service time reduction, there are different portions of the day having different service demands. For example, in the morning the traffic demand is mostly uni-direction and in the upward motion; whereas, in the afternoon the traffic demand is the opposite. By changing the characteristics of the service, service can be improved by decreasing the waiting time and service time for the majority of the people demanding the service.
One of the special cases of service improvements is in regards to the down-peak traffic. Down-peak traffic is defined as the flow of traffic, usually in the afternoon, when a majority of the building population leave the building. The characteristics of this flow are such that people enter the cars at the upper floors and enter car calls which cause the car to move in the down direction and the destination, in almost all cases, is the lobby.
Currently, cars travel to the uppermost landing having a down hall call and start collecting people floor by floor as the car travels down. The problem with this operation is that during the down peak period, the demand for service is high; therefore, cars load up in most cases after the first three or four stops and almost in all cases load up before they reach the bottom third of the building. This results in large waiting times for the passengers in the lower section of the building. Using this method of operation, the elevator system services the building from top to bottom meaning the lower floors only get service if the upper floors are satisfied. This is called lower landing starvation.